Modern utility vehicles—towing vehicles and trailer vehicles—are equipped with a pneumatic brake system, which is at a higher level than an electronic brake system. Moreover, an anti-lock control is provided, with which locking of the wheels during braking is prevented. For this purpose, brake cylinders of service brakes are pressurized and vented via electronically actuated solenoid valves as required by the designated regulations. The solenoid valves are actuated via an electronic control unit, which receives all the data necessary for the actuation of the brakes, including the operation of a brake pedal by the driver and the data from revolution rate sensors (also referred to as ABS sensors) at wheels of the vehicle.
The trailer vehicle is connected to the towing vehicle via a supply pressure line, a control pressure line and an electric line. Data are also transmitted via the electric line.
In the trailer vehicle, there is a reservoir container with a reservoir container pressure, so that a compressed air supply for actuation of the brakes of the trailer vehicle is available even after the disconnection of the supply pressure line.
The trailer vehicle comprises so-called spring-loaded brakes. Once the reservoir container pressure falls below a limit value, brake cylinders of the spring-loaded brakes are automatically vented and the trailer vehicle is braked. During this the wheels can lock.
The trailer vehicle is equipped with a further emergency brake function. In the event of the supply pressure line between the towing vehicle and the trailer vehicle being cut off, the brake cylinders of the spring-loaded brakes are also automatically vented, so that the trailer vehicle is braked. The wheels can lock in this case as well.
Typically, the trailer vehicle comprises a dedicated electronic control unit for the brakes, which also receives digital brake signals from the towing vehicle via the electric line.
In EP 1 538 054, a brake system of a trailer vehicle is represented, with which for the case of automatic braking by means of spring-loading, the wheels on one side lock, whereas anti-lock control is effective for the wheels on the other side.